Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Cucumber (Cucumis sativus) -- Angular Leaf Spot
 
Cause: Pseudomonas syringae pv. lachrymans, a bacterium that overwinters in diseased plant material and on seed. It is spread by rain, sprinkler irrigation, and on workers' hands and clothing. In recent years, using tolerant cultivars has reduced disease incidence.
Symptoms: Leaves, stems, and fruit may be affected. The leaf spot is irregularly shaped with a water-soaked appearance; bounded by the leaf veins the shapes of spots are angular. Bacteria may ooze from the spots in droplets which dry to a white residue. The water-soaked area later turns gray and dies. Often, dead tissue is torn away from the healthy portion, leaving large, irregular holes. Water-soaked spots on fruit are smaller than on leaves, and they are circular. Lesions usually are superficial, but the injury may permit entry of soft-rot organisms. Affected tissue becomes white and may crack open.

Note the numerous lesions on this leaf.

 
Cultivar Resistance: Pickling cultivars 'Regal', 'Royal', 'Pioneer', 'Express', 'Calypso', 'Cross Country', and 'Frontier' have shown tolerance under Washington and Oregon conditions. Slicing cultivars 'Victory', 'Bel Aire', 'Raider', 'Encore', 'Poinsett 76', 'Slice Nice', 'Dasher II', 'Turbo', 'Quest', and 'Sprint-N' are resistant.
Cultural control: The following control program is a combination of those used in other areas.

  1. Use clean, bacteria-free seed.
  2. Practice a 2-year rotation out of cucurbits.
  3. Plant resistant cultivars.
  4. Stay out of wet, infected fields.
  5. In the Hermiston area, do not irrigate with water draining from another cucumber field.
Chemical control:
  1. Applying fixed copper products has reduced disease spread but reportedly has caused some stunting and leaf chlorosis in Oregon.
    1. Cuprofix Ultra 40D at 1.25 to 2 lb/A on 5- to 7-day intervals. 12-hr reentry.
    2. Kocide 2000 at 1 to 2.25 lb/A or Kocide 3000 at 0.5 to 1.25 lb/A on 5- to 7-day intervals. 24-hr reentry
    3. Kop-R-Spray at 2 to 3 teaspoons/gal water.
    4. ManKocide at 2 to 2.5 lb/A on 3- to 7-day intervals. Do not apply within 5 days of harvest. 24-hr reentry.
    5. Nu Cop 50 WP at 1.5 to 3 lb/A. Do not apply within 1 day of harvest. 24-hr reentry.
  2. Seed treatments may help if affected seed is used.
    1. Hot water treatments with various chemicals (calcium propionate at 4.4 oz/gal water; acidic cupric acetate at 6.7 oz/gal water) for 20 minutes at 122°F reduced the frequency of disease in cucumber seedlings, but did not completely eliminate the pathogen. Hot water alone is not effective.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
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